Calcium-activated potassium channel subunit alpha-1 also known as large conductance calcium-activated potassium channel, subfamily M, alpha member 1 (K_Ca1.1), or BK channel alpha subunit,^[5] is a voltage gated potassium channel encoded by the KCNMA1 gene and characterized by their large conductance of potassium ions (K+) through cell membranes.^[6]

Quick Facts KCNMA1, Available structures ...

KCNMA1
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 2K44, 3MT5, 3NAF
Identifiers
Aliases	KCNMA1, BKTM, KCa1.1, MaxiK, SAKCA, SLO, SLO-ALPHA, SLO1, bA205K10.1, mSLO1, hSlo, potassium calcium-activated channel subfamily M alpha 1, CADEDS, PNKD3, IEG16, LIWAS
External IDs	OMIM: 600150; MGI: 99923; HomoloGene: 1693; GeneCards: KCNMA1; OMA:KCNMA1 - orthologs
Gene location (Human) Chr. Chromosome 10 (human)[1] Band 10q22.3 Start 76,869,601 bp[1] End 77,638,369 bp[1]
Gene location (Mouse) Chr. Chromosome 14 (mouse)[2] Band 14|14 A3 Start 23,339,499 bp[2] End 24,064,559 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in parotid gland saphenous vein tibia Achilles tendon myometrium urethra gastric mucosa tail of epididymis seminal vesicula Brodmann area 23 Top expressed in habenula entorhinal cortex primary motor cortex subiculum medial geniculate nucleus amygdala medial dorsal nucleus lateral geniculate nucleus cerebellar vermis visual cortex More reference expression data BioGPS More reference expression data
Gene ontology Molecular function potassium channel activity metal ion binding voltage-gated ion channel activity ion channel activity protein binding voltage-gated potassium channel activity actin binding calcium-activated potassium channel activity large conductance calcium-activated potassium channel activity identical protein binding outward rectifier potassium channel activity Cellular component integral component of membrane membrane voltage-gated potassium channel complex plasma membrane apical plasma membrane caveola postsynaptic membrane Biological process response to hypoxia urination regulation of membrane potential regulation of ion transmembrane transport negative regulation of cell volume ion transport cellular potassium ion homeostasis response to carbon monoxide response to osmotic stress response to calcium ion potassium ion transport transmembrane transport positive regulation of apoptotic process smooth muscle contraction involved in micturition potassium ion transmembrane transport relaxation of vascular associated smooth muscle ion transmembrane transport Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 3778 16531 Ensembl ENSG00000156113 ENSMUSG00000063142 UniProt Q12791 Q08460 RefSeq (mRNA) NM_001014797 NM_001161352 NM_001161353 NM_001271518 NM_001271519 NM_001271520 NM_001271521 NM_001271522 NM_002247 NM_001322829 NM_001322830 NM_001322832 NM_001322835 NM_001322836 NM_001322837 NM_001322838 NM_001322839 NM_001253358 NM_001253359 NM_001253360 NM_001253361 NM_001253362 NM_001253363 NM_001253364 NM_001253365 NM_001253366 NM_001253367 NM_001253368 NM_001253369 NM_001253370 NM_001253371 NM_001253372 NM_001253373 NM_001253374 NM_001253375 NM_001253376 NM_001253377 NM_001253378 NM_010610 RefSeq (protein) NP_001014797 NP_001154824 NP_001154825 NP_001258447 NP_001258448 NP_001258449 NP_001258450 NP_001258451 NP_001309758 NP_001309759 NP_001309761 NP_001309764 NP_001309765 NP_001309766 NP_001309767 NP_001309768 NP_002238 NP_001258448.1 NP_001240287 NP_001240288 NP_001240289 NP_001240290 NP_001240291 NP_001240292 NP_001240293 NP_001240294 NP_001240295 NP_001240296 NP_001240297 NP_001240298 NP_001240299 NP_001240300 NP_001240301 NP_001240302 NP_001240303 NP_001240304 NP_001240305 NP_001240306 NP_001240307 NP_034740 Location (UCSC) Chr 10: 76.87 – 77.64 Mb Chr 14: 23.34 – 24.06 Mb PubMed search [3] [4]
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BK channels are activated (opened) by changes in membrane electrical potential and/or by increases in concentration of intracellular calcium ion (Ca²⁺).^[7][8] Opening of BK channels allows K⁺ to passively flow through the channel, down the electrochemical gradient. Under typical physiological conditions, this results in an efflux of K⁺ from the cell, which leads to cell membrane hyperpolarization (a decrease in the electrical potential across the cell membrane) and a decrease in cell excitability (a decrease in the probability that the cell will transmit an action potential).

BK channels are essential for the regulation of several key physiological processes including smooth muscle tone and neuronal excitability.^[6] They control the contraction of smooth muscle and are involved with the electrical tuning of hair cells in the cochlea. BK channels also contribute to the behavioral effects of ethanol in the worm C. elegans under high concentrations (> 100 mM, or approximately 0.50% BAC).^[9] It remains to be determined if BK channels contribute to intoxication in humans.

BK channels have a tetrameric structure. Each monomer of the channel-forming alpha subunit is the product of the KCNMA1 gene. Modulatory beta subunits (encoded by KCNMB1, KCNMB2, KCNMB3, or KCNMB4) can associate with the tetrameric channel. Alternatively spliced transcript variants encoding different isoforms have been identified.^[6]

Each BK channel alpha subunit consists of (from N- to C-terminal):

1. A unique transmembrane domain (S0)^[10] that precedes the 6 transmembrane domains (S1-S6) conserved in all voltage-dependent K⁺ channels.
2. A voltage sensing domain (S1-S4).
3. A K⁺ channel pore domain (S5, selectivity filter, and S6).
4. A cytoplasmic C-terminal domain (CTD) consisting of a pair of RCK domains that assemble into an octameric gating ring on the intracellular side of the tetrameric channel.^{[8][11][12][13][14][15][16]} The CTD contains four primary binding sites for Ca²⁺, called "calcium bowls", encoded within the second RCK domain of each monomer.^{[8][11][15][16]}

Available X-ray structures include:

• 3U6N​ – Open structure of the BK channel gating ring^[16]
• 3MT5​ – Crystal structure of the human BK gating apparatus^[8]
• 3NAF​ – Structure of the intracellular gating ring from the human high-conductance Ca²⁺ gated K⁺ channel (BK Channel)^[11]

BK channels are pharmacological targets for the treatment of stroke. Various pharmaceutical companies developed synthetic molecules activating these channels^[17] in order to prevent excessive neurotoxic calcium entry in neurons.^[18] But BMS-204352 (MaxiPost) a molecule developed by Bristol-Myers Squibb failed to improve clinical outcome in stroke patients compared to placebo.^[19] BK channels have also been found to be activated by exogenous pollutants and endogenous gasotransmitters carbon monoxide^[20][21] and hydrogen sulphide.^[22]

BK channels are blocked by tetraethylammonium (TEA), paxilline^[23] and iberiotoxin.^[24]

Researchers have identified a rare disease in humans caused by mutations in the gene.  KCNMA1-linked channelopathy can cause neurological conditions like seizures and movement disorders.^[25] An episode of the Diagnosis TV show, based on a column in the New York Times, was about a young girl with a KCNMA1 disorder that caused transient episodes of muscle weakness.^[26]

• BK channel
• Calcium-activated potassium channel
• Voltage-gated potassium channel